Dr. Emile Christian Hansen first isolated the Saccharomyces carlsbergensis at the Carlsberg Brewery in Copenhagen around 1888. S. carlsbergensis is used in the production of several types of beers including lagers. S. cerevisiae is used for the production of ales and conducts top fermentation, in which the yeast rise to the surface of the brewing vessel. In modern brewing many of the original top fermentation strains have been modified to be bottom fermenters. Currently the S. carlsbergensis designation is not used, the S. cerevisiae classification is used instead.  The fermentation of wine is initiated by naturally occurring yeasts present in the vineyards. Beer was known to mankind much before the discovery of the role of yeast. The most neglected ingredient used in making beer is the yeast and the famous Reinheitsgebot (German Beer Purity Law of 1516) didn't even mention yeast. Yeast is an extremely hardy organism and without knowledge of people, it just stuck to the crevises of the brewing equipment and fermented into beer. People believed it was a miracle. Louis Pasteur first became famous for studying the yeast used by European breweries, in an effort to help them make better beer.  Even after the role of yeast in fermentation was discovered, it was just called "Godisgood" and there is an old german saying, "Hopfen und malz, Gotterhalts." which when translated means "We provide the hops and the malt, God takes care of the rest." Ethanol is a valuable alternative to petroleum as a fuel and as a raw material for the manufacturing of many important commercial chemicals.

Yeast is cultured in huge bins under anaerobic conditions. Yeast converts the sugar in grapes to alcohol and carbon dioxide. A one-way valve allows the carbon dioxide to escape without letting any oxygen in. The bubbles are left dissolved in the bins when making sparkling wines such as Champagne. One yeast cell can approximately ferment its own weight in glucose in an hour. The yeast can produce an average of 15 to 16% of ethanol by weight. S. cerevisiae can produce up to 18 percent ethanol, by volume Any more ethanol is toxic to the cells and causes yeast cell lysis. Sulphur dioxide is added to kill naturally present bacteria and molds.  There are basically two major kinds of yeast used in brewing. Ale yeast works at about room temperature, ferments quickly, and produces the pleasant "fruitiness" characteristic of most ales. Lager yeast works at cold temperatures (30 to 40 degrees Fahrenheit), ferments more slowly, and produces the clean taste of a lager beer. Within each of these two types are literally hundreds of different strains of yeast.